a) Field of the Invention
This invention relates to a whitening powder as a skin-care external composition, and more specifically to a whitening powder equipped with good stability of a whitening ingredient, high liquefiability into a form similar to a skin lotion or cosmetic emulsion when spread and rubbed in use despite its being in a powder form, and excellent readiness and feeling of use.
b) Description of the Related Art
Various whitening ingredients have conventionally been applied to the skin in attempts to prevent or reduce UV-induced spots and freckles, resulting in reports of cosmetics, medicines and the like which contain whitening ingredients [for example, C. Fox, Cosmetics & Toiletries, 103, 31-35 (1988); S. S. Bleehen, J. Soc. Cosmet. Chem., 28, 407-412 (1977); Herman E. Jass, Cosmetics & Toiletries, 94, 52-53 (1979); etc.]. The term "whitening ingredient" as used herein means a substance which lightens eumelanin to exhibit skin-depigmenting action, specifically to act in such a way as fading or otherwise lightening spots, freckles and the like on the skin.
Such whitening ingredients however include those prone to decomposition or modification when brought into contact with water. To assure the stability of these whitening ingredients, they have been commercialized in the form of powder-formed compositions. Specifically, these powder-formed compositions are marketed in the name of "Bihaku-powder (=whitening powder)" in Japan [see Walter Luckewicz et al., J. Soc. Cosmet. Chem., 41, 359-367 (1990)].
To use these conventional whitening powders, however, it is necessary to either dissolve or disperse them in water or skin lotion beforehand. These whitening powders are hence accompanied by problems in that they cannot be used with ease, their effective ingredients may be hardly soluble depending on the mixing ratio with water, and their application readiness may be seriously impaired if water is added in an excessive proportion conversely. Moreover, it is also the current situation that, when spread on the skin, they give a poorly-spread tight feeling and a good feeling of touch is barely present.
As a solution to the above-described problems in the readiness of use, the present inventors found a powder-formed composition in which an oil ingredient, an aqueous ingredient and the like have been powderized by making use of hydrophobicized silicic acid anhydride and a powder coated with a fluorine compound. Based on the finding, patent applications were filed under Japanese Patent Applications Nos. HEI 4-46752, 4-321946 and 5-19232. The fluorine-compound-coated powder employed in these patent applications is available by coating a powder, which is suited for use in cosmetics, with a fluorine compound such as perfluoroalkyl phosphate diethanol amine or perfluoroalkylsilane so that the powder is imparted with water-repelling property and oil-repelling property. This powder-formed composition is readily liquefied when spread and rubbed, thereby bringing about a significant improvement in the readiness of use. In addition, it is also excellent in the stability of effective ingredients. Its use as a whitening powder is therefore advantageous. However, due to the use of the oil ingredient and the fluorine-compound-coated powder, an organoleptic problem is still involved in that it is prone to give a poorly-spread tight feeling and/or it may become uneven.
There is accordingly an outstanding demand for the provision of a whitening powder capable of providing still better feeling of use while retaining excellent readiness of use.